Selective hydrogenation of acetylene in ethylene



pound Jhaving the general formula;

SELECTIVE HYDROGENATION OF ACETYLENE IN E'IHYLENE Ludo K. Frevel,Midland, and Leonard J. Kressley, Saginaw, Mich., assignors to The DowChemical Company, Midland, Mich, a corporation of Delaware No Drawing.Filed Sept. 17, 1959, Ser. No. 840,508

9 Claims. (Cl. 260-677) presence of acetylene is undesirable and stepsmust be taken to remove it. i

.It is known that acetylene can be hydrogenated and procedures have beendescribed for the selective hydrogenation of acetylene in anacetylene-ethylene mixture by the use of a palladium catalyst.Relatively good results in selective hydrogenation are obtained with apalladium catalyst, but substantial proportions of the acetylene may notbe hydrogenated without either converting some of 'the acetylene toethane or also hydrogenating a part of the initial ethylene inthemixture. While the amount of the acetylene and ethylene converted to'ethaneis decreased by the use of an improved palladium catalyst,

such as described in the United States Letters Patent No.

2,802,889, issued to applicants of the instant application,

litis desired to further enhance the hydrogenation of the acetylene sothat the acetylene in the mixturelcan be "substantially hydrogenatedwithout the conversion of either the acetylene or the ethylene'in themixture to ethane.

, It is among the objects of the present invention to provide animproved process for the selective hydrogenation of acetylene in amixture containing acetylene and i ethylene. A further object is toprovide an improved process for1 the selective hydrogenation ofacetylene employing a palladium catalyst whereby the hydrogenation ofthe acetylene is enhanced and the hydrogenation of the ethyleneinhibited. H K 1j The above and otherwobjects aretattained according tothe invention, by intermixing a haloaromatic com- I a the palladiumcatalyst. The presence of the haloaromatic compound in the mixturefacilitates the hydrogenation V the catalyst.

'lectivcly hydrogenated to ethylene.

2,981,768 Patented Apr. 25, 1961 of the acetylene to ethylene whileinhibiting the hydro genation of the ethylene. The haloaromatic compoundplaced in the acetylene-ethylene mixture is not retained by thecatalyst. Since the compound is notretained by the catalyst, it does nothave a permanent effect upon The amount of the haloaromatic compoundintermixed 200 parts by volume of the compound per million parts of theacetylene-ethylene mixture.- When more than 200 parts of the compoundper million parts of the gas mixture are used, the activity of thecatalyst may be decreased to the extent that all of the acetylene maynot be hydrogenated. While as little as 10 parts per million of thecompound in the gas mixture markedly improves or enhances thehydrogenation of the acetylene, it is generally preferred to have from40 to parts per million of the haloaromatic compound in the feedmixture.

The presence of the limited amount of the haloaromatic compound not onlyimproves the selectivity of the known palladium hydrogenation catalysts,but it further improves the selectivity of palladium catalysts to whichother metals have been added to improve the catalysts selectivity. Forexample, the selectivity of palladium catalyst which may consist of from1 to 40 parts by lar to that used in contacting an acetylene andethylene mixture with a palladium catalyst is used, except that alimited amount of the haloaromatic compound is added prior to contactingthe mixture with the catalyst. A gas stream of the ethylene, containingacetylene to be removed, is intennixed with a gas stream of hydrogen,unless an excess of hydrogen is already present in theethylene-acetylene mixture, and from 10 to 200 parts by volume of ahaloaromatic compound, such as monoor dihalobenzene, monoordihalotoluene, and monoor dihaloethylbenzene, per million parts of themixture, are

added. The resulting mixture is passed into contact with the palladiumcatalyst whereby the, acetylene is se- The gas mixture may containother, materials, such as hydrocarbons, normally incident to thepreparation of ethylene-containing gas, as well as nitrogen, carbondioxide, and small portions of air and water vapor.

The proportion of hydrogen which should be present in, or' be added to,the ethylene gas is at least that pro'pon tion necessary to hydrogenateall of the acetylene present in the rnixture,i.e., 1 'mole of more, ofhydrogen per mole of acetylene. A slight excess of hydrogen over thattheoretically necessary to react with all the acetylene is usuallyrequired in the practical operation. .Usually it is preferred to employthe minimum proportion of hydrogen that satisfactorily "removes theacetylene from the treated gas product.

The temperature necessary in the reaction zone wherein the acetylene ishydrogenated depends largely on the activity of the palladium catalyst.Certain catalysts are active at room temperature, while othercatalystsmayre quire a reaction temperature of about 250 C. Generally,temperatures of from 60 to about 200 C. are preferred.

The pressure of the gas in the hydrogenation reaction zone does notappear to be critical and can be above or below atmospheric pressure.

The following example further illustrates the invention;

Example A palladium catalystcontaining 0.2 Weight percent.

palladium and 0.002 weight percent silver prepared in a.

manner similar to that described in US. Patent No. 2,802,889, was usedin the selective hydrogenation of a mixture containing acetylene andethylene. The catalyst, in an amount of 15 milliliters, was placed in aglass reactor tube centimeters long having an internal diamthroughorifice meters under constant pressures maintained by constant-headbubbling column in each line. The acetylene stream was passed through acharcoal absorber to remove acetone and through a chromic acid scrubberto remove any phosphines or arsines. The three separated gas streamswere brought together and mixed, and the resulting mixture was passedthrough a bed of basic lead acetate to remove any sulfides. In thismanner a stream of ethylene containing 4 percent acetylene, and 6percent hydrogen was obtained. This stream was passed over themilliliters of the catalyst at a rate of 330 milliliters per minutewhile the catalyst was maintained at a temperature in the range of 140to 150 C.

The product stream issuing from the reactor was analyzed by a massspectrometer for ethane formation and by colorimetric means foracetylene.

In passing the stream free of o-dichlorobenzene through the catalystbed, a product was obtained which contained approximately 2 volumepercent of ethane and acetylene could be detected. O-dichlorobenzene wasthen intermixed with the ethylene stream in an amount of to 50 parts ofthe dichlorobenzene to a million parts of ethylene mixture. The ethanein the product decreased to 0.75 volume percent in minutes and noacetylene could be detected. After operating in this manner for twohours, the addition of o-dichlorobenzene was-discontinued. Upondiscontinuing the addition of o-dichlorobenzene, acetylene could soon bedetected in the product.

The above run was repeated a number of times except that a differentchlorinated aromatic was used in place of o-dichlorobenzene.Monochlorobenzene, monobromobenzene and dibromotoluene were used andsimilar results to that above were obtained.

What is claimed is:

1. In a process for the selective hydrogenation of acetylene in a mixingcontaining ethylene and acetylene wherein the mixture with hydrogen in aproportion greater than 1 mole of hydrogen per mole of acetylene iscontacted with a palladium catalyst, the improvement of enhancing thehydrogenation of the acetylene and inhibiting the hydrogenation ofethylene which comprises the step of intermixing the mixture beforecontacting it with the palladium catalyst with a haloaromatic having thegeneral formula:

where R is a member of the group consisting of hydrogen and alkylradicals having from 1 to 2 carbon atoms, X represents a halogenselected from the group consisting of chlorine and bromine, and n is aninteger selected from the group consisting of 1 and 2 in proportions offrom 10 to200 parts by volume of the haloaromatic compound per millionparts of the mixture.

2. A process according to claim 1 wherein the chlorinated aromaticcompound is o-dichlorobenzene and is intermixed with the mixture inamount of from 40 to 100 parts by volume of o-dichlorobenzene permillion parts by volume of the mixture.

3. A process for the selective hydrogenation of acetylene in a mixturecontaining acetylene and ethylene, which comprises intermixing themixture with a haloaromatic compound having the general formula:

where R is a member of the group consisting of hydrogen and alkylradicals having from 1 to 2 carbon atoms, X represents a halogenselected from the group consisting of chlorine and bromine, and n is aninteger selected from the group consisting of 1 and 2 in proportions offrom 10 to 200 parts by volume of the haloaromatic compound per millionparts of the mixture and with hydrogen in a proportion greater than 1mole of hydrogen per mole of acetylene in the mixture, passing theresulting mixture in contact with a catalytic body containing aneffective proportion of a composite metal material wherein are from to99 parts by weight of palladium and from 40 to 1 by weight of silver.

4. A process according to claim 3 wherein the haloaromatic compound iso-dichlorobenzene.

5. A process according to claim 4 wherein the acetylene and ethylenemixture is intermixed with from 40 to 100 parts by volume ofo-dichlorobenzene per million parts of the mixture.

6. A process according to claim 3 wherein the haloaromatic compound ismonochlorobenzene.

7. A process according to claim 6 wherein the acetylene and ethylenemixture is intermixed with from 40 to 100 parts by volume ofmonochlorobenzene per million parts of the mixture.

8. A process according to claim 3 wherein the hal aromatic compound ismonobromobenzene and is intermixed in proportions of from 40 to 100parts of monobromobenzene per million parts of the mixture.

9. A process according to claim 3 wherein the haloaromatic compound isdibromotoluene and is intermixed in proportions of from 40 to 100 partsof dibromotoluene per million parts of the mixture.

Lindlar June 22, 1954 Frevel et a1. Aug. 13, 1957

1. IN A PROCESS FOR THE SELECTIVE HYDROGENATION OF ACETYLENE IN A MIXING CONTAINING ETHYLENE AND ACETYLENE WHEREIN THE MIXTURE WITH HYDROGEN IN A PROPORTION GREATER THAN 1 MOLE OF HYDROGEN PER MOLE OF ACETYLENE IS CONTACTED WITH A PALLADIUM CATALYST, THE IMPROVEMENT OF ENHANCING THE HYDROGENATION OF THE ACETYLENE AND INHIBITING THE HYDROGENATION OF ETHYLENE WHICH COMPRISES THE STEP OF INTERMIXING THE MIXTURE BEFORE CONTACTING IT WITH THE PALLADIUM CATALYST WITH A HALOAROMATIC HAVING THE GENERAL FORMULA: 